the Cyclostomes is more or less convoluted, and the parts are held together by mesentery-like structures. The hepatogastric ligament ties the stomach to the liver, the gastrosplenic ligament connects stomach and spleen, the hepatoduodenal ligament unites duodenum and liver.
Though the mesenteries of the rat have doubtless evolved from a simpler arrangement, such as that found in the dogfish, they are relatively complex, and require careful study.
The mesogastrium of the rat is expanded into the form of a sac, the greater omentum, which projects backward from the stomach region. The rim of this sac unites with the stomach upon a line extending from the pylorus along the greater curvature of the stomach, around the left end and back to the esophagus on the lesser curvature. Dorsad the greater omentum unites with the body wall between the adrenal glands. The omental sac thus comprises two limbs, a dorsal one united anteriorly with the dorsal abdominal wall, and a ventral limb attached to the greater curvature of the stomach.
The spleen is suspended along its median surface to the left side of the omental sac. It lies parallel to the greater curvature of the stomach. The part of the great omentum connecting the spleen and stomach is the gastrosplenic or gastrolienal ligament. A part of the pancreas is lodged in the descending limb of the great omentum.
The descending colon lies in the sagittal plane of the body. It is held in this position throughout its length by the relatively narrow mesocolon, which joins the dorsal abdominal wall just beneath the inferior vena cava. The mesocolon terminates about three and one-half centimeters from the anus. Anteriorly it fastens on the left to the great omentum. The duodenocolic omentum connects the descending colon and the ascending limb of the duodenum.
